The present invention relates to an endoscope apparatus, a method for operating an endoscope apparatus, and the like.
A depth of field as deep as possible is required for an endoscope apparatus so that the user can easily perform diagnosis and treatment. In recent years, however, an image sensor having a large number of pixels has been used for an endoscope apparatus, and a decrease in depth of field has progressed. In view of this situation, an endoscope apparatus that implements an autofocus (AF) process (operation) has been proposed. The methods described below have been proposed with regard to AF technology that is applied to a video in order to prevent a situation in which a focus operation is unnecessarily performed.
For example, JP-A-2006-208818 discloses a method that stores an AF evaluation value when the focus operation has been completed, and resumes the focus operation when a change equal to or larger than a given threshold value has continued for a time equal to or longer than a given standby time with respect to the AF evaluation value. JP-A-2006-208818 thus prevents a situation in which the focus operation is performed unnecessarily frequently.
JP-A-2010-176061 discloses a method that sets an AF area to the center area of an image, and calculates the degree of similarity in the peripheral area of the image and the degree of similarity in the center area (AF area) of the image from the current image and the previous image after completion of the focus operation. The degree of similarity is a value that decreases as the images are more similar to each other. The focus operation is not performed when the degree of similarity in the peripheral area of the image is equal to or larger than a given threshold value, and the degree of similarity in the center area of the image is equal to or smaller than a given threshold value. JP-A-2010-176061 thus prevents a situation in which the focus operation is unnecessarily performed when the distance to the main object that is situated in the center area of the image does not change even when the object situated in the peripheral area of the image has changed due to a change in framing (after the object has been brought into focus), for example.
It is desirable that an endoscope apparatus be configured so that the field of view is fixed when the user performs treatment, and the focus operation is stopped after the object has been brought into focus.